In a so-called cloud system in which services and applications are provided for users over a network, physical servers operates various Virtual Machines (VMs). When the physical servers operate VMs, the prediction of the operation of each VM is hard because the operations of the VMs vary depending on services and applications provided by the VMs. Thus, the estimation of resources such as Central Processing Units (CPUs) and memory used by the VMs is also hard.
When the memory resources become scarce, the performances of the physical servers decrease due to slashing. In a virtual memory environment, the slashing occurs when the inputs and outputs between physical memory and virtual memory including secondary memory, external memory and auxiliary memory frequently occur due to insufficient memory and the CPU does not accept external processing.
When memory resource becomes scarce, the source physical server moves predetermined virtual machines to a destination physical server. When the physical server moves the predetermined virtual machines to another physical server, memory in the source physical server which has been used by the moved virtual machines is released. Therefore, the source physical server can use the released memory. When the move of the predetermined virtual machines to the destination physical server is completed, the destination physical server can start to operate. Hereinafter, a physical server is referred to as information processing apparatus.
The following patent document describes conventional techniques related to the techniques described herein.